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Onan 6.5NH Exhaust Leak Question


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  #1  
Old 02-05-2018, 01:40:28 AM
mvimpvm mvimpvm is offline
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Default Onan 6.5NH Exhaust Leak Question

Hey all, got a quick question. I have an exhaust leak that is messing up my paint job. Has a new metal OEM gasket on there but still a leak. Anybody got any suggestions? I attached a picture. It is the joint about 4 inches above the flex pipe. That is not a shadow but carbon from exhaust on my paint.
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Old 02-05-2018, 02:27:23 AM
nothingbutdarts nothingbutdarts is online now
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Default Re: Onan 6.5NH Exhaust leak question

Try to file both flanges flatter than high temp. silicone on both sides upon assemble, let dry and go.
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Old 02-05-2018, 02:29:06 AM
geezer88 geezer88 is offline
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Default Re: Onan 6.5NH Exhaust leak question

My NH6.5 leaked in the same place. The flanges were badly warped, so no gasket would hold. I use a grinder to flatten the flanges and all is well.

tom
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Old 02-05-2018, 08:05:36 AM
Max Thompson Max Thompson is offline
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Default Re: Onan 6.5NH Exhaust leak question

I agree with both above posts. Flanges must be "flat" in order to seal.

It looks like you are also leaking at the flex connection. Looks like some black showing around the clamp. That is a tough joint to make air tight. You may have to weld the flex to the tail pipe.
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Old 02-05-2018, 09:08:53 AM
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Billy J Shafer Billy J Shafer is offline
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Default Re: Onan 6.5NH Exhaust leak question

That was a common problem with RV units. Take and grind the flange down flat. That was what we always did. On the pipe we split it or had it welded. That was a hard place to seal off. Some times two clamps around the section worked.
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Last edited by Billy J Shafer; 02-05-2018 at 10:07:04 AM.
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Old 02-05-2018, 09:53:42 AM
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Default Re: Onan 6.5NH Exhaust leak question

Did you have to split the flex to make it go over the pipe ?
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Old 02-05-2018, 10:13:40 AM
consolenut consolenut is offline
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Default Re: Onan 6.5NH Exhaust leak question

I doubled the metal gasket. Then used the orange high temp RTV on it. No issues so far.
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Old 02-05-2018, 09:12:55 PM
mvimpvm mvimpvm is offline
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Default Re: Onan 6.5NH Exhaust leak question

Did you all just use something like a 7" angle grinder with a flat wheel to do the grinding or just a flat file?
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Old 02-05-2018, 09:25:13 PM
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Default Re: Onan 6.5NH Exhaust Leak Question

A grinder or a file. Will work just depends on how much room you have.
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Old 02-05-2018, 11:19:49 PM
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Default Re: Onan 6.5NH Exhaust Leak Question

It seems to me that these flanges are getting bent by over tightening in the past. I'd think it would be best to first try to bend them back as much as possible, then finish by grinding, thereby leaving as much material intact as possible. Maybe even provide relief around the bolt holes, so that the sealing surfaces contact first. Then just snug up the bolts enough to clamp the gasket, but not so much as to bend the flanges again. Those should have been made with thicker flanges and / or more bolts.
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